1. Field of the Invention
The present invention relates to an image forming device which is used in a copy machine, a printer, a facsimile machine, a digital Multi Function Peripheral (MFP) or the like and forms an image of a character, a figure or the like onto printing paper. More specifically, the present invention relates to an image forming device which can prevent toner fused on the printing paper from being removed or smeared.
2. Description of the Related Art
An electrophotographic image forming device is used in, for example, a copy machine, a printer, a facsimile machine, and a digital MFP including a plurality of functions such as a copy function, a printer function, a fax communication function and a scanner function. In such an image forming device, a uniformly charged electrophotographic photoconductor is selectively exposed according to image information, and an electrostatic latent image is formed. A developing device develops the electrostatic latent image, and a toner image is formed. The toner image is transferred onto printing paper (printing sheet). Then, the toner image, which has been transferred onto the printing paper but is yet to be fused, is fused onto the printing paper as a permanent image by a fusing device. The printing paper having the toner image fused thereon is transported from a transportation path to a paper output path by a pressure roller provided in the fusing device. Then, the printing paper is output onto a paper output tray by a paper output roller arranged at an end portion of the paper output path.
In such a conventional image forming device, the pressure roller and the paper output roller generally transport the printing paper having the toner fused thereon through the curved transportation path and the paper output path along a transportation guide, which defines the transportation path and the paper output path, at the same linear speed. Then, the printing paper is output onto the paper output tray. While the printing paper is being transported, an image printed side of the printing paper may make contact with the transportation guide, which defines an inner side of the curved transportation path. Immediately after the toner has been fused on the printing paper, the toner is not fixed completely. Therefore, if the image printed side of the printing paper makes contact with the inner transportation guide, the toner may be removed or smeared.
To prevent the toner from being removed or smeared while the printing paper is being transported, a known image forming device prevents the image printed side of the printing paper from making contact with the inner transportation guide. In such a known image forming device, a linear speed of the paper output roller is slower than a linear speed of the pressure roller. As a result, the transported printing paper bends, and the image printed side of the printing paper does not make contact with the inner transportation guide.
In the conventional image forming device, when carrying out a duplex printing operation in which an image of a character, a figure or the like is printed on both sides of the printing paper, first, a printing operation is performed on a first side (front side) of the printing paper. Then, the paper output roller carries out a switchback transportation of the printing paper. The paper output roller reverses a transportation direction of the printing paper, and the printing paper is transported through a reversal path. Then, the printing paper is transported into an image forming unit again by a duplex transportation roller. A toner image is transferred onto a second side (reverse side) of the printing paper, and the fusing device fuses the toner image. Then, the printing paper is transported to the paper output path by the pressure roller and output onto the paper output tray by the paper output roller. During this switchback transportation, the linear speed of the paper output roller and a linear speed of a duplex transportation roller generally have the same linear speed. In addition, after the printing operation has been performed on the second side, the linear speed of the pressure roller and the linear speed of the paper output roller are also the same. Accordingly, also in this case, the transported printing paper may make contact with the transportation guide, which defines the transportation path, the paper output path and the reversal path.
In the case of performing a duplex printing operation on the printing paper as described above, after the first side of the printing paper has been printed, the transportation direction of the printing paper is reversed and the printing paper is transported to the reversal path. In this case, if the first side having the image printed thereon makes contact with the inner transportation guide, the toner fused on the first side may be removed. Furthermore, after the second side of the printing paper has been printed, the printing paper is transported from the transportation path to the paper output path. In this case, if the first side of the printing paper makes contact with an outer transportation guide, which has been heated by a radiant heat of a heat roller, the toner fused on the first side may be remelted and removed. Therefore, the conventional image forming device does not prevent the toner from being removed or smeared when a duplex printing operation is performed on the printing paper. There is no currently available image forming device which solves this problem.